Spider mites

What's happening

Spider mites are pinhead-sized sap-suckers that love croton, especially in the warm, dry air of a heated home. They cluster on the leaf undersides, pierce the cells, and drain them, leaving leaves looking dull, dusty, and stippled with tiny pale dots. In a bad infestation they spin fine silk webbing across the leaf joints and stem tips, and the plant weakens and drops leaves as they multiply fast.

How to fix it

Isolate the plant away from your others right away, since mites spread quickly. Rinse it down in the shower or sink, hitting the undersides of the leaves hard to knock off as many mites and webs as you can. Then treat thoroughly with neem oil, coating every surface including the undersides and stem joints, and repeat every five to seven days for several weeks to catch newly hatched mites. Raising the humidity around the plant afterward makes it far less hospitable to the next generation.

This is general guidance based on common symptoms; individual plants vary.